Var measuring device



AUS- 11, 1953 A. J. PETZINGER 2,648,821

VAR MEASURING DEVICE Filed Jan. 29, 1948 ATTORNEY Patented Aug. 11, 1953VAR MEASURING DEVICE Ambrose J. Petzinger, Fair Lawn, N. J., assignor toWestinghouse Electric Corporation, East Pittsburgh, Pa., a corporationof Pennsylvania Application January 29, 1948, Serial No. 5,118

Claims. l

This invention relates to phase-shifting devices, and it has particularrelation to var meters including phase-shifting devices for supplyingsuitable voltages thereto.

Although the invention is applicable to circuits operating at variousfrequencies and having various configurations, it will be described withreference to a three-phase three-wire system operating at a frequency ofsixty cycles per second. The invention is suitable for var metersemploying various conventional movements, such as electrodynamic,induction or thermal movements, and the meters may be designed asindicating, integrating or recording meters. The invention will bediscussed with particular reference to var meters employing thermalmovements.

In accordance with the invention, a threewinding transformer is employedas a phase shifter. The transformer includes two primary windings whichare connected for energization in accordance with separate line voltagesof a three-phase three-wire circuit. The secondary winding of thetransformer is responsive to the Vector sum of the magnetic fluxesproduced by the two primary windings. By properly connecting the primarywindings, the Voltage derived from the secondary winding is inquadrature with one of the voltages of the associated threephasecircuit. Consequently, the output of the secondary winding may beapplied to the voltage terminals of a thermal meter which is employedfor measuring the reactive power of the threephase circuit. In order toobtain a complete measurement of reactive power, two phase shifters maybe employed for energizing the voltage terminals of a two-elementpolyphase meter. In addition, current transformers may be required forenergizing the current terminals of the meter.

It should be noted that a thermal meter presents a fixed resistance loadto the transformers.- By properly selecting the ratio of primary leakagereactance to primary resistance of the transformers, it is possible tosubstantially eliminate phase displacement error in the voltagetransformers. Furthermore, the aforesaid ratio may be selected forcompensating for phase displacement errors in the current transformers.

The invention also contemplates the testing of a polyphase meter. In aspecific embodiment of the invention, two elements of a polyphase -meterare connected for energization from a single-phase circuit for testpurposes.

It is, therefore, an object of the invention to provide an improvedphase shifting device.

It is a further object of the invention to provide a phase-shiftingdevice in the form of a transformer having two primary windingsassociated with a common secondary winding.

It is also an object of the invention to provide a measuring deviceincluding a thermal wattresponsive meter energized in part through aphase-shifting device of the type set forth in the preceding twoparagraphs.

It is an additional object of the invention to provide a transformerhaving a fixed resistance load wherein phase displacement error issubstantially eliminated.

It is another object of the invention to provide an improved system forenergizing a polyphase measuring device from a single-phase source ofelectrical energy for test purposes.

Other objects of the invention will be apparent from the followingdescription taken in conjunction with the accompanying drawing, inwhich: Figure 1 is a schematic View of a measuring device embodying theinvention, and

Figs. 2 and 3 are vector diagrams showing voltage and currentrelationships suitable for the measuring device of Fig. l.

The specific measuring device herein described is designed for themeasurement of the reactive power of a three-phase three-wire electricalcircuit. The device is accurate provided that the phase voltages of thethree-phase circuit always remain equal in magnitude and balanced orsymmetrical with respect to phase. However, it should be pointed outthat all conventional reactive power measuring devices depend to thesame extent on these assumptions. As a matter of fact, the variations inmagnitude and balance of the phase voltages of modern electricalvdistribution systems are so small that the accuracies of the reactivepower measuring devices are well within acceptable limits.

Referring to the drawing, Fig. 1 shows a measuring device M which may belocated in a conventional detachable meter casing having eight terminalsin the form of contact blades BI, B2, B3, B4, B5, B6, B'l and B8. Suchcasings are well known in the art and may be similar to the casingillustrated in Fig. 10 of Catalog Section 42-210, published by theWestinghouse Electric Corporation of East Pittsburgh, Pa., November 17,'1941. The contact blades of the meter casing are designed for receptionin the contact jaws of a conventional meter socket, such as thatillustrated in Fig. 17 of the aforesaid catalog section. See also Patent2,297,833. The contact jaws of a suitable socket are represented in Fig.

'1 byvcontact jaws J l to J 8, inclusive.

It will be understood that external circuits applying energy to themeasuring device are connected to the contact jaws. For example, in Fig.1, the measuring device is to be energized from a three-phase three-wirecircuit represented by phase conductors I, 2 and 3. The phase conductorI is interruptedv and has one portion connected to the contact jaws J Iand J2, whereas the remaining portion is connected to the contact jawJ5. Similarly, the phase conductor 3 is interrupted and one portion isconnected to the contact jaws J3 and Jd, whereas the remaining portionis connected to the contact jaw J 8. The phase conductor 2 is connectedto the contact jaws J6 and J7.

The measuring device M is intended to measure the reactive power of theassociated polyphase circuit. In discussing the invention, aconventional system of notation will be employed. Currents derived fromthe phase conductors I, 2 and 3 are identified, respectively as currentsI1, Iz and I3. The voltage between the phase conductors is representedby the symbol El accompanied by a subscript formed by the numerals ofthe phase conductors between which the voltage is taken. For example,the voltage E21 represents the voltage between the phase conductors 2and I. A reversal of the numerals in the subscript indicates a reversalin phase of the voltage represented thereby. As shown in Fig. 2, by anarrow A a conventional counterclockwise rotation of the vectorsrepresenting the three phase voltages is assumed and the phaseconductors have been numbered in accordance with such phase rotation.

From Blondels theorem the instantaneous real power P of the three-phasecircuit may be represented by the following expression:

The instantaneous reactive power of the circuit may be obtained byrotating the voltages in Equation 1 rthrough an angle of 90, asrepresented by the following expression:

The conventional vector operator y indicates a rotation of theassociated voltage through an angle of 90. This rotation is in acounterclockwise direction (represented by -l-i) or in a clockwisedirection (represented by the operator i) depending on whether leadingor lagging reactive power is to be measured. In most cases, themeasuring device would be designed for measuring lagging reactive power.

From Equations 1 and 2, it will be observed that in order to measurereactive power a voltage -y'Esz is desired which is in quadrature withthe line voltage E32.

the form of a three-winding transformer having two primary windings 9aand 9b and a common secondary winding 9c. The three'windings surround,respectively, the three legs of a magnetic core Sid which has a figureof 8 shape. The primary winding 9a is connected across the contactblades B2 and B1 for energization in accordance with the voltage E12.The primary winding 9b is connected across the contact blades B2 and B3for energization in accordance with the voltage E13. When energized, thewindings 9a and 9b produce magnetic fluxes e512 and p13. As shown bydotted arrows in Fig. 1, the vector sum of these fluxes passes throughthe secondary winding Sc and induces in the secondary The desiredvoltage is ob .tained from a phase-shifting device 9 which is in windinga voltage proportional to the vector sum of the voltages E12 and Ein.These voltage relationships are illustrated in Fig. 2, wherein thevoltage E12 and the voltage E13 are vectorially added to provide aresultant voltage e. It will be observed that the resultant voltage e isin quadrature with the voltage E32, and consequently may be lemployed asone of the voltages in Equation 2. It will be understood that thepolarities of energization of the windings are selected to provide thedesired vector addition.

In a somewhat similar manner, a phase-shifting device II is employed tosupply a voltage in quadrature with the voltage E12. The polarities areselected to provide an induced voltage E in the secondary winding I Iewhich is equal to the vector sum of the voltages E131 and E132.Consequently, as shown in Eig. 2, the resultant voltage E is inquadrature with the voltage E112 and may be employed as another of thevoltages required for Equation 2. In addition, the cur-rents I1 and I3may be derived from the conductors I and 3 in any suitable manner asthrough current transformers I3 and I5.

The instantaneous reactive power of the threephase circuit isrepresented by the expression In this expression lc is a constant. Forthe vec; tor relations of Fig. 2, k may be equal to 1\"/3. It will beunderstood that the current I1 and the voltage E may be applied to awatt responsive device for measuring the quantity E11. Also the voltageand the current I3 may be supplied to any conventional watt responsivedevice for measuring the quantity els. By adding the two measurementsthe desired reactive power Q is obtained. Alternatively the voltages andcurrents may be applied to the voltage and current terminals of anyconventional two-element watt responsive device for measuring directlythe reactive power Q.

In Fig. 1, a two-element watt responsive thermal meter Il is provided.This meter includes two spiral bimetallic springs I9 and 2| which havetheir inner ends connected to a shaft 23. The shaft is mounted forrotation with respect to a supporting structure 25 to move a Vpointer 2lacross a suitable scale 29. The springs I9 and 2l have their outer endssecured to a supporting structure and are oppositely wound with respectto the shaft 23. Consequently, the pointer 2l is actuated in accordancewith the difference in temperatures of the two bimetallic springs.

The temperatures of the bimetallic springs are controlled by fourresistance heaters. Two of the heaters 3l and 33 are positioned tosupply heat to the bimetallic spring I9. The remaining heaters 35 and 3lare positionedto supply heat to the bimetallic spring 2l. Such athermal* meter is well known in the prior art, typical constructionstherefor being shown in the Lincoln et al. Patent 1,300,283 and in theVassar Patent 2,323,738.

The heaters 3| and 35 are connected in series across the terminals ofthe secondary winding I Ic for energization in accordance with thevoltage E. The secondary winding of the current transformer I3 has oneterminal connected to a center tap on the winding IIc and a secondterminal connected to the right-hand ends of the heaters 3l and 35, asviewed in Fig. 1. Consequently, the heaters 3l and 35 in eect areconnected in parallel across the secondary winding of the currenttransformer I 3. As an example of suitable current and voltagerelationships the heater 3| may be energized in accordance with thevector sum (mfg and the heater 35 may be energized in accordance Withthe vector dilerence 'I'he current IE is that supplied by the secondaryWinding IIc, Whereas the current I1 is that supplied by the secondarywinding ol." the transformer I3.

, In a somewhat analogous manner the heaters 33 and 31 are connected inseries across the secondary winding 9c for energization in accordancewith the current I?. The heaters 33 and 31 also are connected inparallel across the secondary winding of the current transformer I forenergization by the current The connections are such that the heater 33is energized in accordance with the vector sum whereas the heater 3'1 isenergized in accordance with the vector difference When so connected thepointer 21 will indicate on the scale 29 the reactive power of theassociated three-phase circuit.

It is convenient to test a meter oi the type illustrated in Fig. l froma source of single-phase energy which is represented in Fig. l byconductors LI and L2. The terminals or contact blades provided byapplica-nt facilitates such testing. The conductor L2 is divided intotwo portions L2a and L2b. The portion L2a is connected to the contactjaws JI, J2 and J 6 through suitable switches 4I and 43. The portion L2bis connected to the contact jaw J4 through a suitable switch 45. Theconductor LI is connected through a switch 41 to the contact jaw J3 andthrough a switch 49 to the contact jaw J1. In addition, a switch 5I isprovided for connecting the contact jaws J5 and J8. In addition suitabledisconnect switches 53 are provided for disconnecting the phaseconductors I, 2 and 3 from the contact jaws. It will be understood thatinstead of employing a single socket for the connections to thethree-phase circuit and for the connections to the single-phase circuit,a separate test socket may be employed which is permanently connected tothe single-phase circuit through the circuits illustrated in dottedlines in Fig. 1. The measuring device then would be inserted in theauxiliary test socket for test purposes. However, for convenience inillustration, a single socket is assumed to be employed for bothcircuits. n

In order to test the measuring device, the disconnects 53 would be openand the switches 4I, 43, 45, 41, 49 and 5I would be closed. Thisconnects the primaries of the current transformers I3 and I5 in seriesfor energization in accordance with the current supplied from a sourceto a load by the conductors LI and L2. In addition, all of the primarywindings 9a, 9b, .IIa and IIb are connected in parallel across theyconductors LI and L2. The polarities are such that the secondarywinding 9c has a voltage induced therein which is proportional to thesum of the voltages across the windings 9a and 9b. A similar voltage isinduced in the secondary winding IIc. In effect, the thermal meter I1 isdivided into two single-phase elements Which are connected to thesingle-phase circuit represented by the conductors LI and L2.

It will be noted that only eight terminals or contact blades arerequired to provide the desired test facilities. This is advantageousfor the reason that eight Icontact jaws and eight contact blades are themaximum number in one available style of detachable casing and socketunits.

It is well understood in the art that transformers are subject to phasedisplacement errors. By following the principles hereinafter set forth,it is possible to eliminate almost completely the inaccuracies resultingfrom such phase displacement errors.

As shown in Fig. 3, the primary voltage VP applied to the primarywinding of a transformer is equal to the sum of the induced primaryvo-ltage EP and the voltage drops due to the primary resistance Rp andthe primary leakage reactance XL. The primary `current IP may be dividedinto an exciting current and a load current IL. Inasmuch as the lo-adrepresented by the heaters of a thermal meter is a resistive load, theload current IL is substantially in phase with theinduced voltage EP andis so represented in Fig. 3. The exciting current comprises amagnetizing component Io in quadrature with the induced voltage Ep and aloss component in phase with the induced voltage Ep and load `currentIL. Since in a Well designed transformer the loss component is extremelysmall compared to the load current IL, only the magnetizing component ofthe exciting current Io is shown in quadrature with the induced voltageEp in Fig. 3.

The load current IL in traversing the leakage reactance of thetransformer primary produces a voltage drop ILXL which leads the loadcurrent IL by The exciting current component Io in traversing theprimary resistance RP produces a voltage drop IoRP which is in phasewith the exciting current. By inspection of Fig. 3, it will be observedthat the drops ILXL and IoRp are substantially in phase opposition.Consequently, by proper selection of the ratio of the resistance Rp tothe leakage reactance XL, it is possibleV to make the sum of these twovoltage drops Zero. The load current and the exciting current intraversing respectively the primary resistance and the primary leakagereactance produce additional voltage drops ILRP and 10XL. However, theselast two voltage drops are substantially in phase with the inducedvoltage EP. Consequently, the sum VP of the induced voltage EP and thevarious voltage drops is in phase with the induced voltage EP.

If desired, the ratio of the primary resistance to the primary leakagereactance may be selected to compensate at least in part for othererrors. For example, the current transformers I3 and I5 of Fig. 1 mayhave phase displacement errors. If these phase displacement errors aresubstantially constant over the load range of the current transformers,the phase displacement errors of the transformers 9 and II may beadjusted to compensate for the phase displacement errors of the currenttransformers. If the phase displacement errors of the currenttransvinduced voltage EP.

vformers' vary y'over the load range thereof, 'the compensationintroduced -by the voltage transformers 9 and il may be made equal tothe average of the phase'displacement errors introduced by the currenttransformers. In other rent of these transformers.

y The required adjustment for the voltage transformer maybe understoodby reference to Fig. 3. By increasing vthe magnitude or the 'primaryresistance Rp, the voltage drop IoRp may be increased'to make theresultant voltage Vp lag the The same result may be achieved bydecreasing the primary leakage reactance. By decreasing vthe primaryresistance or increasing the primary leakage re'actance, or both, theresultant voltage VP may be made to lead the induced voltage EP. In thisway, the phase displacement between the voltage VP and the load currentIL may be controlled.

The adjustment of the primary resistance and leakage reactance may beeffected in various ways. To change the vprimary resistance the materialemployed in the primary winding may be selected to provide the desiredresistance values. Alternatively, trie resistance of the leads to theterminals of the primary windings may be selected to have the propervalues or adjustable resistors may be connected in series therewith. Theleakage reactance also may be adjusted in various known 'ways as byvarying' the number of tur-ns in 'the windings.

rIt will be observed that the transformers 9 and i i not only serve asphase shifting transformers but also may operate as ratio transformers.The ratio of the number of turns in the Asecondary windings 9c and licrelative to the primary turns may be varied to produce the desiredmagnitude of output voltages e and E. Preferably the turns, leakagereactances and primary resistances of the pair of primary windingsyemployed in each of the transformers 9 and Il should be kept equal.

Although the invention has been described with `reference to certainspecific embodiments there-- of, numerous modifications falling withinthe spirit Vand Scope of the invention are possible.

I claim as my invention: 1. In an electrical device, athree-phase-circuit having three phase conductors, a transformer devicehaving a secondary winding and vhaving two primary windings effectivewhen energized for inducing a voltage in the secondary windingsubstantially proportional to the vector sum of the energizations of theprimary windings, means connecting the primary windingsv forenergization respectively in accordance with the voltages betweenseparate pairs of said 'phase conductors for inducing a voltage in thesecondary winding substantially in quadrature with the voltage betweenthe remaining pair of said phase conductors, translating meansresponsive to two alternating quantities and the vector relationshiptherebetween, and means connecting the translating means for a firstenergization from said secondary winding and a second energization fromthe three-phase circuit.

2. A device as claimed in claim 1 wherein the transl-ating meanscomprises a thermal wattg meter connected to vreceive a voltage inputfrom the secondary winding and av currentinput from one of said phaseconductors.

3. In an electrical device, a three-phasecircuit having threephaseconductors i, 2 and 3 for carrying phase currents I1, I2 and Is,and having when energized voltages E13, E32 and E21 between theconductors represented by the voltage Subscripts, a iirst transformerdevice comprising a magnetic core having three legs magnetically inparallel, a pair of primary windings respectively on two of said legs,and a secondary winding disposed on the third leg of the magnetic core,means connecting the primary windings for energization respectively inaccordance with the voltages E13 and E21 to induce in the secondarywinding a voltage in quadrature with the voltage E32.

4. In an electrical device, a three-phase circuit having three phaseconductors i, 2"and 3 `for carrying phase currents I1, I2 and I3numbered in the order of phase rotation, and having when energizedvoltages E13, E32 and E21 between the conductors represented by thevoltage subscripts, first and second transformer devices each comprisinga pair of primary windings, a secondary winding and a magnetic coreseparately coupling the secondary winding to each of the primarywindings, means connecting the primary windings of the rst transformerfor energization respectively in accordance with the voltages E13 andE21 to induce in the associated secondary Winding a first voltage inquadrature with the voltage E32, means connecting the primary windingsof the second transformer device for energization respectively inaccordance with the voltages E32 and E31 to induce in the associatedsecondary winding a second voltage in quadrature with the voltage E21,and watt-'responsive translating means connected for energization fromthe secondary windings and the three-phase circuit in accordance withthe first and second voltagesand the currents Ir and I3.

5. A device as claimed in claim 4 wherein the translating meanscomprises a polyphase thermal watt-responsive meter having rst heatersconnected for energization from the first voltage and the current I1 andhaving second heaters connected for energization from the second voltageandthe current I3 to produce a meter output representing the reactivevolt-amperes of the three-phase circuit.

6. Inan electrical device, a three-phase circuit havingl three phaseconductors i, 2 and 3 for `carrying phase currents I1, I2 and I3,'andhaving when energized voltagesE13, E32 and E21 between the conductorsrepresented by the voltage subscripts, a rsttransformer devicecomprising a magnetic core having three legs magnetically in parallel, apair of primarynwindings respectively on two of saidlegs, and asecondary winding disposed on the third leg of the magnetic core, meansconnecting the primary windings for'energization respectively inaccordance with 'the voltages E13 and E21 to induce in the secondarywinding a voltage in quadrature with the voltage E32, and means forconnecting the primary windi'ngsfor energization from a pair ofterminals in accordance with a single-phase voltage` 7. A device asclaimed in claim 4, in combination, with means selectively operable forconnecting the primary windings to a pair of conductors energizing allof the primary windings in accordance with a single-phase voltage, andselectively operable means for connecting the'translating means toreplace the currents I1 and I3 by a common single-phase current.

8. In an electrical device, a voltage transformer having primary windingmeans designed for energization at a rated input voltage, a currenttransformer having a phase displacement error, and translating meanshaving separate inputs from said transformers, said translating meansbeing responsive t0 the phase displacement between the outputs of thetransformers, said translating means presenting substantially a fixedresistance load to said transformers, said voltage transformer having aprimary leakage reactance and a primary resistance selected to make themagnitude of the voltage drop resulting from load current flowingthrough the leakage reactance different from the magnitude of thevoltage drop resulting from the exciting current of the voltagetransformer flowing through the primary resistance by an amountsufficient to compensate the translating means for the error introducedby said phase displacement error.

9. In an electrical device, a voltage transformer having primary windingmeans designed for energization at a rated input voltage, and asubstantially fixed resistance load for the transformer, saidtransformer having a primary leakage reactance and a primary resistanceselected to make the magnitude of the voltage drops resulting from loadcurrent flowing through the leakage reactance substantially equal to themagnitude of the voltage drop resulting from the exciting current of thetransformer flowing through said primary resistance.

10. In an electrical device, a three-phase circuit having three phaseconductors, a transformer device having a secondary winding and havingtwo primary windings effective when energized for inducing a voltage inthe secondary winding substantially proportional to the vector sum ofthe energizations of the primary windings, means connecting the primarywindings for energization respectively in accordance with the voltagesbetween separate pairs of said phase conductors for inducing a voltagein the seoondary winding substantially in quadrature with the voltagebetween the remaining pair of said phase conductors, translating meansresponsive to two alternating quantities and the vector relationshiptherebetween, and means connecting the translating means for a :Erstenergization from said secondary winding and a second energization fromthe three-phase circuit, said translating means comprising a thermalwattmeter connected to receive a voltage input from the secondarywinding and a current input from one of said phase conductors, and saidtransformer device comprising a primary leakage reactance and a primaryresistance selected to make the magnitude of the voltage drop resultingfrom load current flowing through the leakage reactance substantiallyequal to the magnitude of the voltage drop resulting from the excitingcurrent of the transformer flowing through said primary resistance.

AMBROSE J. PETZINGER.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 920,652 Ricketts May 4, 1909 1,399,968 Knopp Dec. 13, 19211,944,656 Downing Jan. 23, 1934 1,953,519 'I'ritschler Apr. 3, 19341,971,207 Boyajian Aug. 21, 1934 2,068,575 Stark Jan. 19, 1937 2,121,592Gough June 21, 1938 2,243,162 Lee May 27, 1941 2,358,725 Mauerer Sept.19, 1944 2,424,596 Weber July 29, 1947 2,454,201 Petzinger et al Nov.16, 1948 2,495,158 Carlin Jan. 17, 1950 FOREIGN PATENTS Number CountryDate 111,837 Great Britain Jan. 31, 1918

